The present invention relates to an inflatable impact protection cushion for the occupant of a motor vehicle cushion of disc-shaped form, having a cushion lower part fastened to a fixed vehicle part, in particular to the steering wheel, an inlet opening situated approximately in its center, and a circular cushion upper part which, upon inflation, moves forward away from the cushion lower part and is joined to the latter at the edge.
An impact protection device is shown in German Patent 2,152,902 where the impact protection cushion, intended as protection for the driver of a passenger car, is fixed to the steering wheel by its lower part which has an opening for the inflow of the gas inflating the cushion. On the opposite cushion upper part, an insert is firmly connected to the upper part; the insert is anchored to the steering wheel by cords as restraints. Upon inflation, this impact protection cushion initially opens out in the direction of the gas flow from the steering wheel in the direction of the head area of the driver, until the cords tensioned by the forward movement of the cushion upper part prevent any further forward movement in the direction of the area of the occupant's head. As a result, during the further course of the inflating operation, the impact protection cushion inflates in the transverse direction in a disc-like manner. Such restraining straps prevent the impact protection cushion from moving forwards in a radiating manner parallel to the gas inflow direction at high speed until in the area of the occupant's face.
"Automobiltechnische Zeitschrift", 91 (1989), Page 207, describes an inflatable impact protection cushion for a front passenger, in which tearing seams are arranged in the region of joining seams, which seams join the cushion side walls extending between cushion upper part and cushion lower part, for controlled opening out during inflation. The tearing seams hold together side regions of the protective cushion which are folded against one other so that, when they tear during the cushion inflating operation, in each case parts of the side walls of the cushion successively open out.
A similar tearing seam arrangement is also described in DE 38 18 185 C1 in which the gas can feed in in two different pressure stages. A breaking of the tearing seams does not commence until at the higher pressure stage, whereas the tearing seams hold together in the lower pressure stage. At low deceleration values, therefore, the impact protection cushion opens out only partially. The tearing seams are arranged in the region of adjacent joining seams between side parts and a central part of a protective cushion provided with a rectangular inlet frame and suitable, in particular, for a front passenger.
The present invention has an object of providing with little expenditure an impact protection cushion having favorable opening-out characteristics which is suitable, in particular, also for protecting the driver of a motor vehicle.
This object has been achieved in accordance with the present invention by an impact protection cushion upper part, which in the installed position, is folded onto the cushion lower part and is joined at the latter by at least one tearing seam extending in its central region. Both the opening-out operation and the opening-out speed of the impact protection cushion are advantageously influenced by the arrangement of a seam which joins the cushion lower part and the cushion upper part and can tear open during the inflating operation. The cushion upper part of the present invention remains on the cushion lower part at the beginning of the inflating operation in any event in the region of this seam. An abrupt forward movement of the cushion upper part in the direction of the vehicle occupant due to the inflowing gas stream is thereby prevented.
The effect is achieved that, at the beginning of the inflating operation, the impact protection cushion opens out primarily in the transverse direction, i.e. sidewards and upwards and downwards, before the seam tears and the impact protection cushion opens out completely. The tearing seam arranged in this way consequently compensates for the preferred opening-out in the direction of the vehicle occupant, caused by the inflow direction of the inflating gas, as a result of which the opening-out operation in this direction takes place much more uniformly and with a lower maximum spreading speed.
The improved opening-out characteristics of the present invention ensure a favorable opening-out operation with reduced weight, costs and production effort in comparison with the use of restraining straps, without any contact between opening-out parts of the impact protection cushion and the vehicle occupant to be protected occurring during the opening-out phase.
Another aspect of the present invention has the advantage that the central region of the cushion upper part opposite the gas inflow opening, which region is most likely to move forward quickly and abruptly, is surrounded by the tearing seam.
A configuration of an interrupted tearing seam of the present invention has the effect that the region enclosed by the tearing seam can already be inflated partially through the interruptions before the seam, as such, tears. This makes the operation of the cushion upper part moving forward even more uniform overall. The interruptions also provide favorable points of action for the tearing of the seam so that the tearing operation of the seam itself also does not take place abruptly. This is likewise beneficial for a uniform opening-out operation.
A symmetrical arrangement of the tearing seam with respect to the center point of the cushion upper part can also be provided, by a tearing seam extending coaxially with respect to the edge of a circularly shaped cushion upper part.
In the case of an uninterrupted tearing seam, it is advantageous to provide inflection regions which are suitable, in particular, as points of action for a commencing tearing-open of the seam and prevent an abrupt tearing-open.
According to yet another feature of the present invention, there are provided two tearing seams which require different tearing forces, one of which seams completely encloses the other. The forward movement of the cushion upper part in the direction of the vehicle occupant is made even more uniform as a result. It is determined by two tearing-open operations taking place one after the other. Such a two-stage arrangement of the tearing seams can be additionally refined in accordance with the present invention which refinements are further beneficial for a uniform opening-out operation of the cushion.